The shape of grooves in constant-velocity joints used in automobiles is measured, for example, as follows. A mixture of fine powder and liquid is first applied to a surface to be measured. Then, a spherical body having specified dimensions is pressed against the measurement surface, and a line that is formed accordingly in the contact portion is measured using a caliper, etc. However, such a method requires a complicated operation, with a low accuracy in measuring the shape of grooves.
On the contrary, there are disclosed apparatuses for measuring the shape of a curved surface in Patent Documents 1 and 2. Methods of measuring the shape of a curved surface using the apparatuses described in Patent Documents 1 and 2 will hereinafter be described.
In the measuring apparatus described in Patent Document 1, a spherical portion having the same diameter as a ball to be rolled along a ball rolling groove and formed on a main shaft is first engaged with the ball rolling groove. Next, the main shaft is rotated about the shaft line thereof. Here, the movement of a contact that protrudes from the spherical portion and is in contact with the ball rolling groove is to be measured. This allows the shape of the ball rolling groove to be measured.
In the measuring apparatus described in Patent Document 2, a reference sphere is restrained between the curved surface of a work to be measured and the horizontal and vertical restraining surfaces of a restraining member. In this state, the distance between the reference position of the work and the horizontal restraining surface is measured. This measurement is to be carried out for three reference spheres having their respective different diameters. Then, the curvature radius of the curved surface of the work and the position of the curvature center are calculated geometrically using those measured values.
Patent Document 1: Japanese Utility Model Publication No. S61-17365
Patent Document 2: Japanese Patent Application Laid-Open No. H8-285506